title: Cone thermogenesis and its limits in the tropical Cycas micronesica (Cycadaceae): association with cone growth, dehiscence, and post-dehiscence phases.
abstract: OBJECTIVE
  Thermogenesis is a prominent pollination-related feature of cycad cones and is generally assumed to play a role in pollination. Although typically studied just before, during, and immediately after the cones' pollination phase, thermogenesis may be present in other cone developmental phases. •
  
  
  METHODS
  We assayed thermogenesis in Cycas micronesica, Guam's endangered cycad, over successive cone developmental phases by measuring temperatures in shaded and unshaded in situ cones for up to 7 wk. We also studied the effect of ambient conditions on cone thermogenesis in laboratory experiments and estimated the cones' metabolic heating rates. •
  
  
  RESULTS
  Pollen cones exhibit a continuous, but small, metabolically generated thermogenesis for multiple weeks, including a single thermogenic peak temperature greater than peak ambient each day. The magnitudes of those daily peak temperature elevations above ambient reach maxima twice during cone development: a few days before dehiscence and approximately 1 wk post-dehiscence. Excised cones in dark, fixed temperature environments generated multiple thermogenic events (∼24 h period) over ∼10 d. Cones appear to initiate a protective temperature regulatory response at temperatures ≥∼38°C. •
  
  
  CONCLUSIONS
  Cycas micronesica pollen cones exhibit several thermogenic attributes not reported in other cycads, including continuous thermogenesis for many weeks. These cones grow in a hot tropical environment that likely confines their metabolically generated temperature increases to a small thermogenic window beyond which they encounter heat stress. These findings suggest the presence of thermogenic functions not strictly related to pollination and a potential vulnerability to warming climates.
authors.affiliation: University of Utah, Department of Mechanical Engineering, 50 S. Central Campus Dr., Salt Lake City, Utah, 84112 USA.
authors.forename: Robert B
authors.initials: RB
authors.lastname: Roemer
authors.forename: L Irene
authors.initials: LI
authors.lastname: Terry
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Marler
mesh_terms: D001833:Body Temperature Regulation; D002940:Circadian Rhythm / Q000502:physiology; D029784:Cycas / Q000033:anatomy & histology* / Q000254:growth & development*; D011058:Pollen / Q000254:growth & development* / Q000502:physiology*; D013696:Temperature; D013997:Time Factors; D014329:Tropical Climate
keywords: Cycadaceae; Cycas micronesica; cycads; heat stress; inverse calorimetry; pollination; simulations; temperature; thermogenesis